We will determine if rat lung fibroblasts isolated from normal and bleomycin-treated rats exist as a heterogeneous group of cells with different collagen synthetic rates. The major objective is to provide molecular bases for differences of collagen metabolism in normal and fibrotic rat lung fibroblast subpopulations. The parent cultures will be separated into fibroblast subsets using a cell sorter. The isolated cells will be characterized by determining various collagen synthetic parameters including cellular and polysomal type I and type III procollagen synthesis, secretion, accumulation and degradation, the cellular concentrations of type I and type III procollagen mRNAs and the steady state levels of procollagen mRNAs in nuclei, the post-polysomal cytoplasm and polysomes. The synthetic and degradative rates of total cellular procollagen mRNA species will be determined. The accumulation of newly synthesized procollagen mRNAs in the subcellular fractions will also be determined. Type I and type III procollagen mRNA transcription will be assessed by determining the amounts of type I and type III procollagen hnRNAs and the ability of these nuclei in vitro to synthesize hydridizable type I and type III procollagen mRNAs. The synthesis of nuclear procollagen mRNAs will be determined by incubating fibroblast with (3H) uridine for short periods of time. The rates of transport of these mRNA species into the cytoplasm will be determined. We will also determine the possible heterosensitivity of type I and type III procollagen synthesis in the fibroblast subsets of glucocorticoids and bleomycin. These studies will determine the collagen synthetic rates in fibroblast subsets from normal and fibrotic lung. One fibroblast subpopulation may contribute more collagen in fibrotic lung disease than another subset. This may provide information which will be useful for therapeutic intervention.